1. Field of the Invention
The present invention relates to a method for controlling a clothes dryer, and more particularly to a method for controlling a combined sensing type clothes dryer, capable of preventing an excessive or insufficient drying encountered in single sensing type using temperature sensors or humidity sensors.
2. Description of the Prior Art
Referring to FIG. 1, there is illustrated a general construction of clothes dryer. As shown in FIG. 1, the clothes dryer comprises an outer case 1, a drum 2 rotatably disposed in the outer case 1, and a motor 4 fixedly mounted to the inner wall of outer case 1 above the drum 2 to generate a torque. The torque of the motor 4 is transmitted to the drum 2 via a drum belt 3, to rotate the drum.
The drum 2 has at its front portion a door 14 and a plurality of holes for introducing hot wind in the drum 2. A heater 13 for emitting a heat is disposed forwardly of the drum 2. A plurality of vent holes are formed at the rear wall surface of the drum 2, for venting air with vapor. Inwardly of the vent holes, a filter assembly 15 is attached to the rear portion of the drum 2, so as to separate bits of thread from the air and vapor exhausted out of the drum 2.
A heat exchanging fan 7 is also rotatably mounted, rearwardly of the drum 2. The fan 7 is rotated by receiving the torque from the motor 4 via a fan belt 6. A plurality of vent holes 5 are also formed at the outer case 1, so as to introduce air into the outer case and vent air out of the outer case.
A duct 11 is disposed beneath the drum 2. The duct 11 provides a passage of circulating hot wind extending from the rear portion of the drum 2 to the interior of drum 2 via the heater 13. Accordingly, the hot wind exhausted out of the rear portion of drum 2 is heat-exchanged with outer cold air by the function of the fan 7 and then fed to the interior of drum 2, via the heater 13. A drain port 10 is also provided at a desired portion of the duct 11, outwardly of the outer case 1. Through the drain port 10, condensed water generated during the heat exchange is drained outwardly.
Control for a drying operation of the general clothes dryer with the above-mentioned construction can be conventionally achieved according to two control methods one of which is a temperature sensing type wherein the drying operation is controlled, based on the intake air temperature and the exhaust air temperature of the drum 2 detected by two temperature sensors 9 and 12 attached to the drum 12 and the other of which is a humidity sensing type wherein the drying operation is controlled, based on the humidity detected by the humidity sensor 8 attached to the rear surface of the drum 2, in place of the temperature sensors 9 and 12.
Referring to FIG. 2, there is illustrated a control device for controlling the drying operation of the temperature sensing type clothes dryer. As shown in FIG. 2, the control device comprises an electric power supply unit 21 for supplying electric power to required units of the dryer, a first temperature sensing unit 22 and a second temperature sensing unit 23 for converting, into electric signals, the temperature detection values indicative of the exhaust air temperature and the intake air temperature of the drum 2 detected by two temperature sensors 9 and 12 attached to the drum 12, respectively, an A/D converter 24 for converting the sensing signals from the first and second temperature sensing units 22 and 23 into digital signals, a microcomputer 25 for carrying out the control for the drying operation, based on the sensed temperature values from the A/D converter 24, and a load driving unit 26 for driving the motor 4 and the heater 13, under the control of the microcomputer 25.
In FIG. 2, the same elements as those shown in FIG. 1 such as the motor 4, the temperature sensors 9 and 12 and the heater 13 are denoted by the same reference numerals.
On the other hand, FIG. 3 is a circuit diagram of a control device for controlling the drying operation of the humidity sensing type clothes dryer. As shown in FIG. 3, the control device comprises an electric power supply unit 21 for supplying electric power to required units of the dryer, a humidity sensing unit 27 for converting, into electric signals, the humidity detection value indicative of the exhaust air humidity of the drum 2 detected by the humidity sensor 8, an A/D converter 24 for converting the sensing signal from the humidity sensing units 27 and 23 into a digital signal, a microcomputer 25 for carrying out the control for the drying operation, based on the sensed humidity value from the A/D converter 24, and a load driving unit 26 for driving the motor 4 and the heater 13, under the control of the microcomputer 25.
In FIG. 3, the same elements as those shown in FIG. 1 such as the motor 4, the humidity sensor 8 and the heater 13 and as those shown in FIG. 2 such as the electric power supply unit 21, the A/D converter 24, the microcomputer 25 and the load driving unit 26 are denoted by the same reference numerals.
Now, the drying operation of the clothes dryer will be described, in conjunction with the control operations according to the control devices of the above-mentioned types.
When the dryer is operated after the user puts clothes into the drum 2, the microcomputer 25 turns on the motor 4 and the heater 13 via the load driving unit 26.
As the motor 4 is driven, its torque is transmitted to the drum 2 via the drum belt 3 so that the drum 2 rotates at a relatively low and uniform rate. Simultaneously, the torque motor 4 is also transmitted to the heat exchanging fan 7 via the fan belt 6, so as to rotate the heat exchanging fan 7.
Accordingly, the heater 13 emits heat which is, in turn, supplied to the interior of the drum 2. As a result, the internal temperature of the drum 2 increases and the moisture contained in the clothes is evaporated and exhausted out of the drum 2 via the filter assembly 15. The air exhausted out of the drum 2 undergoes an heat exchange with outer cold air introduced into the outer case 1 by the rotation of heat exchanging fan 7. By the heat exchange, the vapor contained in the warm exhaust air is condensed into water which is, in turn, discharged out of the drain port 10 along the duct 11. The exhaust air from which the moisture is separated is then fed to the heater 13, so as to be circulated to the drum 2 at a heated state. As the drying operation is continued for a predetermined period of time in a manner as mentioned above, the moisture contained in the clothes is continuously evaporated. With the lapse of time, the evaporation amount is gradually increased.
The drying operation is carried out in a manner as mentioned above. Where such a drying operation is controlled by the temperature sensing type control method, the first temperature sensor 9 attached to the rear surface of drum 2 detects the temperature of the exhaust air and the second temperature sensor 12 disposed near the heater 13 detects the temperature of the intake air which has been free of the vapor, but does not pass the heater 13 yet. In this case, the drying operation is controlled by controlling turning on/off of the heater 13, based on the detected intake air temperature and the detected exhaust air temperature.
With the lapse of drying operation time, for example, the detected temperatures by the temperature sensors 9 and 12 are increased due to the heat emission of the heater 13, as shown in FIGS. 4 and 5. When a predetermined period of time has elapsed, the heat amount emitted from the heater 13 and the evaporation amount become constant, thereby causing the variation in temperature detected from the temperature sensors 9 and 12 to be constant. That is, a constant drying interval occurs at the point of time when the variation in temperature becomes constant. Such a constant drying interval does not occur, when the drying load, namely, the fabric quantity of clothes to be dried is small.
FIG. 4 shows temperature curves S1 and S2 which illustrate the variations in temperature detected by the temperature sensors 9 and 12, depending on the drying time, in cases of small and large fabric quantities, respectively. The patterns 1 of FIG. 4 show the cases when the fabric quantity is small. In these cases, the evaporation amount is small relative to the emitted heat amount of the heater 13, so that the exhaust air temperature is rapidly increased and thereby reaches the control temperature T.sub.peak of the heater 13. That is, the time tw taken to reach the control temperature T.sub.peak is lesser for a smaller fabric quantity.
On the other hand, the patterns 2 of FIG. 4 show the cases when the fabric quantity is large. In these cases, the evaporation amount is slowly increased at the early stage of the drying operation, so that the detected temperatures by the temperature sensors 9 and 12 are increased. When the heat amount emitted from the heater 13 and the evaporation amount become constantly proportional to each other, the detected temperatures by the temperature sensors 9 and 12 become constant. In the pattern 2, the curve S1 shows the variations in temperature sensed by the first temperature sensor 9, whereas the curve S2 shows the variations in temperature sensed by the second temperature sensor 12.
As the moisture quantity of the clothes is suddenly reduced, the exhaust air temperature is increased. At this time, the temperature curve S2 indicating the temperature sensed by the second sensor 12 has an increasing gradient lower than that of the temperature curve S1 indicating the temperature sensed by the first temperature sensor 9. As a result, the gap between the temperature curves S1 and S2 is increased.
The difference G.sub.L between the temperatures sensed by the temperature sensors S1 and S2 in the pattern 1 of a small fabric quantity is larger than the difference G.sub.S between the temperatures sensed by the temperature sensors S1 and S2 in the pattern 2 of a large fabric quantity.
In accordance with the temperature sensing type control method, therefore, the drying operation time t is checked after the drying operation is begun by turning on the motor 4 and the heater 13, so as to check whether a predetermined time t has been elapsed. When the predetermined time t has elapsed, the temperature S1 of the exhaust air containing vapor and the temperature S2 of the intake air free of the vapor, but not heated by the heater 13 yet are sensed by the temperature sensors 9 and 12, respectively, so that the difference between the exhaust air temperature S1 and the intake air temperature S2 is calculated (.DELTA.T=S1-S2). Where the temperature difference .DELTA.T is more than a predetermined value T1 (a constant value calculated experimentally previously and stored) at the point of time when the predetermined time t1 has been elapsed or the exhaust air temperature S1 reach the heater control temperature T.sub.peak within the predetermined time t1, the fabric quantity is determined to be small. In this case, a timer operation is carried out, by which the drying operation is achieved for a predetermined time (a reference time calculated experimentally previously and set). Following the timer operation, the heater 13 is turned off and the drum 2 and the fan 7 are rotated for a predetermined time (a time for cooling the heated clothes calculated experimentally previously and set), so as to cool the heated clothes. Thereafter, the motor 4 is turned off, to complete the drying operation.
However, where the exhaust air temperature S1 does not reach the heater control temperature T.sub.peak within the predetermined time t1 and the temperature difference .DELTA.T is not more than a predetermined value T1 at the point of time when the predetermined time t1 has been elapsed, the fabric quantity is determined to be large. In this case, the drying operation is continued and the temperature difference .DELTA.T sensed by the temperature sensors 9 and 12 is continuously checked. When the temperature difference .DELTA.T is more than a predetermined value T2, the heater 13 is turned off and only the drum 2 is rotated for a predetermined time (a time for cooling the heated clothes at a large fabric quantity, calculated experimentally previously and set), so as to cool the heated clothes. Thereafter, the motor 4 is turned off, to complete the drying operation. The predetermined value T2 is a constant value calculated experimentally previously and set to correspond to the temperature difference at the point of time when the drying degree is not less than 97% at a large fabric quantity. The predetermined value T2 is more than the predetermined value T1.
On the other hand, in accordance with the humidity sensing type control method, the humidity in the drum 2 is sensed by the humidity sensor 8 attached to the rear surface of drum 2. In the humidity sensing unit 27, the detected value from the humidity sensor 8 is converted into an analog signal which is, in turn, converted into a digital signal by the A/D converter 24. The digital signal is then applied to the microcomputer 25. Accordingly, the microcomputer 25 controls the drying operation, based on the sensed humidity.
In accordance with the humidity sensing type control method, the drying operation is begun as the motor 4 and the heater 13 are turned on and the drum 2 and the fan 7 are rotated, in a manner similar to the temperature sensing type control method. With the lapse of drying operation time, the evaporation amount is gradually increased.
When a predetermined time t.sub.H1 has been elapsed, for example, the variations in humidity as shown by the patterns 1 and 2 of FIG. 7 occur, depending on the fabric quantity.
Where the fabric quantity is small (pattern 1), the humidity H1 is sharply increased, as compared with the case where the fabric quantity is large (pattern 2). When the predetermined time t.sub.H1 has been elapsed and the emitted heat amount of the heater 13 and the evaporation amount are constantly proportional to each other, the humidity H1 is kept at predetermined levels H.sub.8 and H.sub.A in respective cases of a small fabric quantity and a large fabric quantity (constant humidity interval). Following the constant humidity interval, the evaporation amount, namely, the vapor amount is suddenly reduced, thereby causing the humidity H1 to be sharply decreased. As the humidity H1 is decreased to reach a humidity sensing limit H.sub.S, the heater 13 is further driven for a predetermined time. Thereafter, the heater 13 is turned off, to complete the drying operation.
FIG. 8 shows the variation in resistance of the humidity sensor depending on the ambient temperature and the relative humidity. As shown in FIG. 8, the resistance of the humidity sensor is decreased, as the relative humidity increases. Also, the effect of the ambient temperature on the resistance is more increased at a higher relative humidity. The resistance becomes small at a higher ambient temperature and large at a lower ambient temperature. At the relative humidity of 90%, for example, the variation in resistance may be large, depending on the variation in ambient temperature. However, the variation in resistance is very small at the relative humidity of about 10%.
Where the fabric quantity is large as in the pattern 2, the sensed humidity is relatively high, since the area of generating vapor is large, as compared with the pattern 1 with a small fabric quantity. At the large fabric quantity, the decreasing rate of the evaporation amount is low, as compared with the case with small fabric quantity. As a result, a long operation time is required at the large fabric quantity.
In accordance with the drying operation controlling method using the humidity sensor, the drying operation is begun by turning on the motor 4 and the heater 13, as shown in FIG. 9. When the drying operation time t has passed a predetermined time t.sub.H1, an operation for sensing the humidity H1 is begun and a determination is made about whether the sensed humidity H1 is less than the humidity sensing limit Hs. When the sensed humidity H1 is less than the humidity sensing limit Hs, the time is counted so that the heater 13 and the motor 4 are maintained at their On states, respectively, until a predetermined time (the time taken for the humidity to be 0%) has elapsed. When the predetermined time has been elapsed, the heater 13 is turned off. Thereafter, the drum 2 and the fan 7 are driven again for a predetermined time, so as to cool the heated clothes. Following the cooling operation, the motor 4 is turned off, so as to complete the driving operation.
However, the above-mentioned temperature sensing type and humidity sensing type control methods have various problems. Where the fabric quantity is too large, for example, the temperature difference .DELTA.T sensed by the temperature sensors 9 and 12 increases no longer, even when the drying of clothes has been actually completed. Accordingly, the temperature sensing type control method in which the drying operation is controlled, based on the temperature difference .DELTA.T has a problem of an excessive drying, in that the point of drying completion time can not be found. At a larger fabric quantity, the temperature difference .DELTA.T increases more slowly, thereby resulting in an excessive drying.
This is because the heat from the heater 13 is shielded by the clothes due to the large quantity of clothes and thereby difficult to be transmitted to the vicinity of the first temperature sensor 9. This phenomenon occurs remarkably at a larger fabric quantity or in cases of large volume clothes or blankets.
Even at the same fabric quantity, the temperature difference .DELTA.T (S1-S2) sensed by the temperature sensors 9 and 12, namely, the temperature gap may occur, depending on the ambient temperature. In particular, the temperature difference .DELTA.T increases more at a lower ambient temperature. As a result, the conventional control method wherein the fabric quantity is determined by the temperature gap has a problem of a considerable error in the fabric quantity determination. In some cases, an ambient temperature sensor is additionally provided for sensing the ambient temperature around the dryer. In this case, there is also a problem that the fabric quantity should be determined by compensating the sensed temperature difference, so as to reduce the fabric quantity determination error.
In the humidity sensing type method, the relative humidity can be sensed only within a range of 10% to 90%, as shown in FIG. 8. Beyond the range, the humidity sensing operation becomes inaccurate or impossible. The humidity sensor 8 senses hardly the humidity, at a lower ambient temperature. At the ambient temperature of 0.degree. C., the sensing operation of the humidity sensor 8 is impossible. At a higher ambient temperature, an error increases more, since the humidity of ambient air is high. The humidity is also affected by a generation of gas, the quantity of wind generated by the fan 7 and a vibration.
In cases of commercially available clothes dryer, the humidity sensors are difficult to determine a very small fabric quantity, since the relative humidity ranges from 0% to 10% at the very small fabric quantity. At the fabric quantity, the humidity sensed by the humidity sensor reaches early the humidity sensing limit Hs, so that an insufficient drying state occurs. When the fabric quantity is excessive, the relative humidity may exceed 90%. In this case, it is difficult to determine accurately the fabric quantity by checking the humidity.